A cellular wireless communication system, as shown in FIG. 1, is mainly comprised of a User Equipment (UE), an access network and a Core Network (CN). A network comprised of eNodeBs, or eNodeBs and base station controllers is referred to as a Radio Access Network (RAN), which is responsible for transactions of an access layer, such as radio resource management. A physical or logical connection may exist between eNodeBs, and each eNodeB can be connected to one or more CN nodes. The CN is responsible for transactions of a non-access layer, such as location update, etc., and is an anchor point of a user plane.
In the cellular wireless communication system, wireless coverage of a fixed eNodeB network is limited due to various reasons, for example, coverage leaks exist inevitably in the wireless network coverage due to barrier of various building constructions to wireless signals. In addition, at edge regions of a cell, due to attenuation of wireless signal strength and interferences between adjacent cells, communication quality of the UE is poor and the error rate of the wireless transmission will increase when the US is at edges of the cell. In order to improve data transmission throughput, group mobility, temporary network deployment, throughput at edge regions of the cell and coverage of a new area, at present, a solution is to introduce a wireless network node, which is referred to as a relay, in the cellular wireless communication system.
The relay is a station which relays data between other network nodes through a wireless link, which is also referred to as a relay node/relay station, and its working principle is shown in FIG. 2. A UE which is directly served by the eNodeB is referred to as a macro UE, and a UE which is served by the relay is referred to as a relay UE. A wireless link between the eNodeB and the UE is referred to as a direct link, including an uplink/downlink (DL/UL) direct link; a link between the relay and the UE is referred to as an access link, including a DL/UL access link; and a wireless link between the eNodeB and the relay is referred to as a backhaul link, including a DL/UL backhaul link.
There are a number of methods for the relay to relay data, for example, directly amplifying a radio signal from the eNodeB; or processing data transmitted by the eNodeB accordingly to forward to the UE, wherein the processing may be demodulation or decoding; or the eNodeB and the relay cooperatively transmitting data to the UE, and conversely, the relay also relaying the data transmitted from the UE to the eNodeB.
Among many types of relay, there is one type of relay, which has the following characteristics.
A UE can not distinguish cells under a relay and a fixed eNodeB, i.e., from the perspective of the UE, there is no difference between the cell under the relay and the cell under the fixed eNodeB. Such a cell under the relay may be referred to as a relay cell. The relay cell, like all the other cells, has its own Physical Cell Identity (PCI), and transmits broadcast like ordinary cells. When the UE resides in the relay cell, the relay cell can individually allocate and schedule radio resources to the UE for use, and the resource scheduling of the relay and radio resource scheduling of the eNodeB (which is also referred to as a Donor eNodeB, i.e., the eNodeB to which the relay is connected by a backhaul link) participating in relay are independent of each other. The interface and protocol stack between the relay cell and the relay UE are the same as those between an ordinary eNodeB cell and an ordinary UE.
The current Long Term Evolution (LTE) cellular wireless communication system, as shown in FIG. 3, uses an Internet Protocol (IP) based flattened architecture, and is comprised of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), Evolved Packet Core (EPC) nodes and other support nodes. The EPC nodes include a Mobility Management Entity (MME), a Serving Gateway (S-GW) and a Packet Data Network Gateway (P-GW). The MME is responsible for control plane signaling, including control plane related operations, such as mobility management, non-access layer signaling processing, user mobility management, context management, etc. The S-GW is responsible for transmitting, forwarding, route handover of UE user plane data. The eNodeBs (eNBs) are logically connected via an X2 interface, and are used to support the mobility of the UE within the entire network to ensure seamless handover of the user. The P-GW is a node which connects the EPC with a packet data network (such as Internet), and is responsible for assigning an IP address of the UE, filtering IP data packets by service type into service data flows and binding the service data flows to a corresponding transmission bearer, and so on.
Each eNB is connected to a System Architecture Evolution (SAE) core network via a S1 interface, i.e., is connected to a MME via a control plane S1-MME interface, is connected to a S-GW via a user plane S1-U interface. The S1 interface supports multipoint connections between the eNB and the MME and S-GW. The MME and the S-GW are connected via a S11 interface, the S-GW and the P-GW are connected via a S5 interface, and the eNBs are connected via an X2 interface. Each eNB transmits signaling and data to the UE through an Uu interface. After the relay is introduced, the wireless interface between the relay and the eNB is the Un interface. The interface between the relay and the UE, like the interface between the eNB and the UE, is also an Uu interface.
Current relays are divided into three categories: fixed relays, nomadic relays, and mobile relays. Both the fixed relays and the nomadic relays are fixedly deployed, and the difference between them is that the nomadic relays can support plug and play, and are more convenient to deploy than the fixed relays. The mobile relays themselves have certain mobility, and in typical application scenes, the mobile relays are deployed on vehicles, such as trains, cars, etc., to facilitate provision of better services for the UE in the vehicles. As for mobile handover, the mobile relay, as a convergence network element, converges a large number of simultaneous movements of the UE into a movement of a network element, i.e., the mobile relay, thus reducing the overhead of signaling in the air interface and the network during handover.
However, based on the above deployment requirements of the mobile relay, the existing technology can not yet provide a mobile wireless relay system supporting the mobile relay and a handover method based on the mobile relay, thereby bringing inconvenience to practical applications.